This invention relates to a hydraulically actuated valve train for an internal combustion and more particularly to an improved high efficiency device for such applications.
With the present emphasis on high specific outputs for internal combustion engines while at the same time maintaining good fuel economy and accurate control of emission of unwanted exhaust gas constituents, it is desirable to optimize all features of the engine. One of the features that is very limiting in engine performance is the valve train. Conventional valve trains employ a camshaft and a mechanical system that interconnects the cam lobes with the poppet type valves for actuating the valves. The mechanical complexity of such devices is believed to be obvious.
In addition to the mechanical complexity, the mechanically operated systems have presented certain limitations as to the speed at which the valves may be opened and closed and also as to the effective valve timing. In addition, the clearances of the mechanism, which may vary during running conditions such as under temperature changes, make it accurate to control the valve operation under all of these circumstances.
To offset many of these deficiencies, it has been proposed to provide a hydraulic system wherein the valves are actuated hydraulically. Such an arrangement is shown in U.S. Pat. No. 2,306,131, entitled "Hydraulic Valve Lifting Mechanism", issued Dec. 22, 1942. The arrangement shown in that patent provides an extremely good valve actuating mechanism that offsets many of the disadvantages noted above. However, this device employs a mechanically operated plunger that pressurizes hydraulic fluid, namely lubricating oil, and delivers it to a fluid motor that is associated with the individual valves for operating the valves. The plunger is supplied with lubricating oil under pressure which is, in turn, delivered through a distributor arrangement. The plunger serves two functions in the arrangement shown in that patent. First, it operates as the pressurizing device and second, it operates as a valve so as to cut off the communication of the chamber in which the plunger reciprocates from the remainder of the distributor so as to trap the fluid in the line that leads to the valve. Where these two functions are combined in a single device, there are several disadvantages that result. Specifically, the maximum opening and closing rates are compromised and furthermore the lift of the valve cannot be controlled as accurately as desired. In addition, certain problems may be experienced on starting up.
It is, therefore, a principal object of this invention to provide an improved valve actuating mechanism for an internal combustion engine.
It is another object of this invention to provide an improved hydraulic valve actuating mechanism for an internal combustion engine wherein the sequence of valve events may be accurately controlled under all running conditions.